Compound Interest - General Questions

A sum amounts to Rs. 5,100 in 2 years and to Rs. 6,375 in 3 years at compound interest. What is the rate of interest?

Find the amount on Rs. 16,000 for 3 years at 20% per annum compounded annually.

What is the compound interest on Rs. 4,800 at 10% per annum for 2 years, compounded annually?

What is the compound interest on Rs. 15,600 at 15% per annum for 2 years, compounded annually?

A sum of money doubles itself at compound interest in 6 years. In how many years will it become eight times?